A methodological approach for determining the effect of moisture content on the compaction properties of powders: Granular hydroxyapatite

The effect of moisture on the compaction properties of hydroxyapatite (HA) was studied. A single lot of commercially available HA was heated at various temperatures to provide samples containing 2.12, 4.02, 4.56, 4.97 and 5.26% moisture content as determined by thermogravimetric analysis (TGA) at 450 °C. Compressibility, compactibility, elastic recovery and Youngʹs modulus of elasticity were determined as a function of moisture content. An increase in moisture content increased the compressibility coefficient of HA facilitating volume reduction at constant compaction pressure. However, increased moisture content also reduced the bonding capacity of HA particles, resulting in reduced tablet tensile strength at constant porosity. Elastic recovery increased and Youngʹs modulus of elasticity decreased, with increasing moisture content, which contributed to reduced tablet tensile strength. The plasticising effect of moisture was outweighed by the reduction in bonding capacity and the increase in elastic behaviour, resulting in a negative effect of moisture on tablet tensile strength over the range studied.